The present invention relates in general to automatic stop motion apparatus for looms for detecting broken warp yarns or threads, and more particularly to electro-optical apparatus for electrically stopping high speed looms when a broken thread defect or the like occurs in the warp threads on the loom in a thread supply direction from the heddle zone by projecting a light beam through the open shed of the warp sheet from one side of the warp sheet and detecting variations in the light beam at the opposite side of the warp sheet by a photoelectric detector head and electronic circuitry which responds only to predetermined light variations occurring when the shed is open to produce a stop signal when an improperly shaded warp occurs.
Heretofore, the most prevalent stop motion apparatus for detecting defects in the warp shed formed by a loom have been of the drop bar or drop wire type, involving a thin flat plate or the like which is suspended for each warp thread at a predetermined location along the warp sheet and is designed to fall from the supporting warp thread or yarn at the time the break of the corresponding warp thread occurs. Usually, the drop wires are positioned behind the heddle frames so that there necessarily occurs a lag in detection and hence in the stopping of the loom, allowing a lag time wherein the breaking end the thread has the opportunity to entangle around the adjacent threads and form an improper warp shed which causes the formation of floats or distortions which disturb regular shading motion of the warp yarns and produce weaving defects in the resultant fabric. Such floats have often prevented the drop wires of the conventional warp stop motion system from falling down, so that the warp stop motion is rendered inoperative in these instances.
More recently, electrical or electro-optical warp loom stop motion systems have been proposed. U.S. Pat. No. 2,279,675 to Gutman discloses a warp stop motion system wherein a beam of light is projected transversely relative to the warp sheet at a position to pass through the open shed when the warp shed is in open position, together with a photoelectric detector and a mechanism which is controlled in timed relation to the rotation of the main drive shaft of the loom and thus in predetermined time relation with the opening of the shed to permit defect signals from the photoelectric detector to operate the loom stop mechanism only when the shed is in a predetermined open condition, thus preventing the photodetector from activating the stop mechanism and producing false stops when the shed is substantially closed. Later U.S. Pat. Nos. 3,379,225 and 3,989,068 have disclosed electro-optical stop motion systems for looms wherein a light beam projector and photodetector are both mounted on the moving sleigh of the loom which executes fore and aft movements through the open space defined by the open shed to detect threads or defects improperly occurring in the open shed during certain portions of the cycle of operation of the loom to produce a loom stopping signal. Of course, the positioning of the light beam producing optics, the photodetector head optics, and such electronic preamplifier circuitry and the like associated with the latter which needs to be mounted on the moving sleigh introduces significant maintenance problems and renders it difficult to provide loom stop motions systems in this manner which remain reliable for relatively long service life periods.
Other systems have been proposed to alleviate the problem encountered in providing a reliable loom stop motion system having adequate service life characteristics such as U.S. Pat. No. 3,818,236 wherein the optical beam is continuously rotated about a horizontal axis along a cylindrical path centered in the open shed and having a large enough diameter to deliberately intersect the upper and lower yarn sheets of the shed four times during each revolution and thereby produce signals which can be processed by circuitry for detecting when additional beam intercepts of thread occur to stop the loom. Also, U.S. Pat. No. 3,902,534 discloses a stop motion system wherein a monitoring light beam is disposed below the lowermost yarn sheet of the shed at the shed opening position and the lowermost yarn sheet is disposed adjacent a rotating brush cylinder close to or in contact with the warp yarn so that when a warp yarn is broken it is immediately arrested by the bristles of the brush and wrapped around the cylinder drawing the broken yarn through the monitoring light beam to activate the stop motion.
An object of the present invention is the provision of a novel stop motion system for looms, wherein a stationary monitoring light beam is projected transversely of the yarn sheet through the open shed and detected by a photodetector head, and wherein novel electronic circuitry is provided for processing the signal produced by the photodetector head to provide an effective processing window for such signals which occurs during a short predetermined time when the shed is open related to the cycle of operation of the loom so as to permit sensing of defect signals only when the shed is in a predetermined open phase, and wherein means are provided to disable the system for producting false stop signals for a predetermined period after machines start up.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawing illustrating a preferred embodiment of the invention.